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The effect of pre-service treatments on the long term properties of 9Cr steels strengthened by boron and nitrogen

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conference contribution
posted on 2017-01-13, 11:45 authored by Anna Sammarco, R. Vanstone, Rachel ThomsonRachel Thomson
Martensitic 9Cr steels have been developed which are strengthened by boron in order to stabilise the microstructure and improve their long-term creep strength. Boron plays a key role in these steels by stabilising the martensitic laths by decreasing the coarsening rate of M23C6 carbides, which act as pinning points in the microstructure. In this work two modified FB2 steel forgings are compared. Both forgings have similar compositions but one underwent an additional remelting process during manufacture. Creep tests showed that this additional processing step resulted in a significant increase in time to failure. In order to investigate the effect of the processing route on microstructural evolution during aging and creep, a range of advanced electron microscopy techniques have been used including ion beam induced secondary electron imaging and High Angle Annular Dark Field (HAADF) imaging in the Scanning Transmission Electron Microscope. These techniques have enabled the particle population characteristics of all the second phase particles (M23C6, Laves phase, BN and MX) to be quantified for materials from both forging processes. These quantitative data have enabled a better understanding of how the processing route affects the microstructural evolution of FB2 steels.


The authors would like to acknowledge the Engineering and Physical Sciences Research Council UK through the Doctoral Training Centre Grant No. EP/G037345/1 and GE Power for financial support of this project.



  • Aeronautical, Automotive, Chemical and Materials Engineering


  • Materials

Published in

8th International Conference on Advances in Materials Technology for Fossil Power Plants


569 - 581


SAMMARCO, A., VANSTONE, R. and THOMSON, R.C., 2016. The effect of pre-service treatments on the long term properties of 9Cr steels strengthened by boron and nitrogen. IN: Parker, J., Shingledecker, J. and Siefert, J. (eds). Advances in Materials Technology for Fossil Power Plants, Proceedings from the Eight International Conference (EPRI 2016), Albufeira, Algarve, Portugal, 11-14 October 2016, pp. 568-580.


© Electric Power Research Institute (EPRI). Distributed by ASM International.


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